A concentrator tube comprises a reflector portion having two walls; and an aperture closing an opening to the reflector portion. The aperture and the reflector portion extend longitudinally. The aperture is substantially flat relative to curvature of the reflector portion.
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32. A concentrator tube extending from a distal end to a proximal end comprising:
a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector portion configured to concentrate light from a source onto an absorber;
a light transmissive aperture member closing the upper opening of the trough shaped reflector portion, wherein the tube concentrates light incident through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 80%; and
the absorber located within the tube;
wherein:
the reflector portion is configured such that substantially any radiation energy emitted from the absorber onto the reflector portion is either directed to the source or directed back to the absorber;
each end of the tube is sealed; and
the reflector portion and the aperture member are formed by rolling a mandrel on an outside surface of a softened glass tube.
29. A method of forming a concentrator tube extending from a distal end to a proximal end, comprising:
forming a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector portion configured to concentrate light from a source onto an absorber;
forming a light transmissive aperture member closing the upper opening of the trough shaped reflector portion; and
positioning the absorber located within the tube;
wherein:
the reflector portion is configured such that substantially any radiation energy emitted from the absorber onto the reflector portion is either directed to the source or directed back to the absorber, and wherein the reflector portion is further configured to compensate for aberrations in the light entering the concentrator tube due to refraction by the aperture member; and
the reflector portion and the aperture member are formed by rolling a mandrel on an outside surface of a softened glass tube.
1. A concentrator tube extending from a distal end to a proximal end, the concentrator tube comprising:
a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector portion configured to concentrate light from a source onto an absorber;
a light transmissive aperture member closing the upper opening of the trough shaped reflector portion, the light transmissive aperture member formed integrally with the trough shaped reflector portion through an extrusion process such that a volume enclosed by the concentrator tube is formed as whole via the extrusion process, wherein the tube concentrates light incident through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 80%; and
the absorber located within the tube;
wherein:
the reflector portion is configured such that substantially any radiation energy emitted from the absorber onto the reflector portion is either directed to the source or directed back to the absorber; and
each end of the concentrator tube is sealed such that the concentrator tube encloses the volume between the trough shaped reflector portion, the light transmissive aperture member, and the sealed ends of the concentrator tube, the volume being substantially evacuated, and
the reflector portion and the aperture member are formed by rolling a mandrel on an outside surface of a softened glass tube.
2. The concentrator tube of
3. The concentrator tube of
4. The concentrator tube of
6. The concentrator tube of
7. The concentrator tube of
8. The concentrator tube of
9. The concentrator tube of
10. The concentrator tube of
11. The concentrator tube of
12. The concentrator tube of
13. The concentrator tube of
14. The concentrator tube of
15. The concentrator tube of
21. The concentrator tube of
22. The concentrator tube of
23. The concentrator tube of
24. The concentrator tube of
26. The concentrator tube of
27. The concentrator tube of
28. The concentrator tube of
30. The method of
forming a seal at each end of the tube to form a substantial vacuum within the tube.
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The present application is a continuation application of U.S. patent application Ser. No. 14/414,010, filed Jan. 9, 2015, which is a national stage entry under 35 U.S.C. § 371 of International Application No. PCT/US2013/032524, filed Mar. 15, 2013, which in turn claims the benefit of U.S. Provisional Patent Application No. 61/670,823, filed Jul. 12, 2012, entitled “SOLAR THERMAL CONCENTRATOR AND METHOD OF FORMING SAME,” the entire contents of each of which are incorporated herein by reference.
The present disclosure relates to solar energy collectors and concentrators and, more specifically, to collectors and concentrators which are thermodynamically efficient without requiring tracking.
Many solar energy systems lack efficiency due to various factors. Additionally, many such systems require expensive tracking capability to track the sun across the sky. Without such tracking, these systems are incapable of collecting sufficient solar energy.
A number of systems for passive or non-tracking reflecting concentration of solar energy have been produced in the past. Among such systems are those shown in U.S. Pat. Nos. 5,537,991; 3,957,041; 4,002,499; 4,003,638; 4,230,095; 4,387,961; 4,359,265; 5,289,356; and 6,467,916 all of which are incorporated here by reference as if set forth fully. It is appropriate to refer to the reflectors as light-transmission devices because it is immaterial whether the reflectors are concentrating radiation from a large solid angle of incidence (e.g. concentrating solar light onto a solar cell) or broadcasting radiation from a relatively small source to a relatively large solid angle (e.g. collecting light from an LED chip to form a beam).
Concentration of radiation is possible only if the projected solid angle of the radiation is increased. This requirement is the direct consequence of the law of conservation of the etendue, which is the phase space of radiation. Solar concentrators which achieve high concentration must track the sun; that is, they must continuously reorient in order to compensate for the apparent movement of the sun in an earth center (Ptolemaic) coordinate system. Reflectors, in contrast, are fixed in position for most lighting purposes. For tracking collectors the direction to the center of the sun is stationary with respect to their aperture. Such concentrators can achieve very high concentrations of about 45000 in air. Even higher concentrations have been achieved inside transparent media.
Tracking, however, is technically demanding because solar collectors are commonly fairly large and designing these systems for orientational mobility may add significantly to their cost. Moreover the absorber, which incorporates some heat transfer fluid as well as piping, also may need to be mobile. This is the motivation to study the concentration which can be achieved with stationary, non-tracking devices. The same principles apply when it is desired to deliver light or other radiant energy from a small source to a relatively large solid angle.
The inventors have realized that a concentrator assembly may be used, e.g., to collect solar energy to produce electrical energy. Embodiments of the concentrator assembly feature a wide acceptance angle, allowing for use in non-tracking applications.
Various aspects of examples of the disclosure are set out in the claims.
According to a first aspect, a concentrator tube is disclosed extending from a distal end to a proximal end including: a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector configured to concentrate light from a source onto an absorber; a light transmissive aperture member closing the upper opening of the trough shaped numbers; and an absorber located within the tube;
In some embodiments, the tube encloses a volume. In some embodiments, the volume is substantially evacuated.
In some embodiments, the reflector portion is located on an interior wall of the volume.
In some embodiments, the reflector portion is located outside of the volume.
In some embodiments, the aperture member is less curved than the reflector portion.
In some embodiments, the aperture member is substantially flat.
In some embodiments, the absorber is positioned to accommodate refraction of light entering the concentrator tube through the aperture.
In some embodiments, the reflector portion is configured to accommodate refraction of light entering the concentrator tube through the aperture.
In some embodiments, the reflector portion is configured such that edge ray light rays refracted by the aperture reflect from the reflector portion and contact the absorber.
In some embodiments, the absorber is configured to have a thermal energy transfer fluid flowing therethrough.
In some embodiments, the absorber includes an input and a output for the thermal energy transfer fluid. In some embodiments, both the input and the output extend through a first end of the concentrator tube.
In some embodiments, the absorber has an end portion located proximal a second end of the concentrator tube. In some embodiments, the end portion is free to move within the tube in response to thermal expansion or contraction.
the absorber includes a plurality of minichannels configured to allow flow therethrough of the thermal energy transfer fluid.
In some embodiments, the tube concentrates light incident through the aperture member at angles to an optic axis less than an acceptance angle.
In some embodiments, the tube concentrates through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 80%.
In some embodiments, the tube concentrates through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 90%.
In some embodiments, the tube concentrates through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 95%.
In some embodiments, the tube concentrates through the aperture member at angles to an optic axis less than an acceptance angle with an optical efficiency greater than 99%.
In some embodiments, the acceptance angle is greater than 10 degrees, 20 degrees, 25 degrees, 35 degrees, or more.
In some embodiments, the absorber includes a heat pipe.
In some embodiments, the absorber includes a u-shaped tube coupled to an absorber fin.
In another aspect, a method of forming a concentrator tube, including: forming a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector configured to concentrate light from a source onto an absorber; forming a light transmissive aperture member closing the upper opening of the trough shaped numbers; and positioning an absorber located within the tube. In some embodiments, the reflector portion is configured such that substantially any radiation energy emitted from the absorber onto the reflector is either directed to the source or directed back to the absorber.
In some embodiments, the reflector portion and the aperture are formed by rolling a mandrel on an outside surface of a softened glass tube.
Some embodiments include forming a seal at each end of the tube to form a substantial vacuum within the tube. In some embodiments, the seal at at least at one end is a metal-to-glass seal.
In another aspect, a method is disclosed including: receiving light from a source using a concentrator tube including: a trough shaped reflector portion extending between the proximal end and the distal end and defining an upper opening, the reflector configured to concentrate light from a source onto an absorber; a light transmissive aperture member closing the upper opening of the trough shaped numbers; and an absorber located within the tube. In some embodiments, the reflector portion is configured such that substantially any radiation energy emitted from the absorber onto the reflector is either directed to the source or directed back to the absorber.
Some embodiments include concentrating light from the source onto the absorber; and converting energy from the light into a thermal energy in the absorber. In some embodiments, the source is the sun.
Various embodiments may include any suitable combination of the above described elements.
For a more complete understanding of example embodiments of the present disclosure, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:
Various configurations of solar collectors and concentrators have been used with varying degrees of efficiency. Thermodynamically efficient concentrators can provide a higher level of concentration of thermal radiation captured by the concentrators. For example, an external compound parabolic concentrator is described in U.S. Patent Publication No. 2012/0073567, which is hereby incorporated by reference in its entirety.
Conventional solar collectors have been designed based solely or primarily on the principles of imaging optics. However, it can be illustrated that the use of imaging optics fails in real-world applications. In this regard, reference is made to
Embodiments of the present disclosure forego imaging optics and, instead, rely upon the principles of thermodynamics. Reference is now made to
F12+F13=1
F21+F23=1
F31+F32=1
A1F12=A2F21
A1F13=A3F31
A2F23=A3F32,
where Ai is the surface area of wall i. These equations can now be solved to obtain:
F12=(A1+A2−A3)/(2A1)
F13=(A1+A3−A2)/(2A1)
F23=(A2+A3−A1)/(2A2).
Referring now to
F14=[(A5+A6)−(A2+A3)]/(2A1)
F23=[(A5+A6)−(A1+A4)]/(2A2).
As illustrated in
Accordingly, a thermodynamically efficient concentrator may be designed with these concepts. In this regard, the above-described concentration problem may be used in reverse to arrive at a thermodynamically efficient concentrator. Referring now to
Next, at block 630, the probability of radiation from the source 510 reaching the aperture 530 is calculated. In this regard, strings are drawn from the ends of the source (a, a′) to the end of the aperture (b, b′). Assume the surface areas are A1 for the source 510, A2 for the aperture 530, A3 for the absorber 540, A4 for the surface formed by a′b, A5 for the surface formed by ab′, A6 for the surface formed by a′b′, and A7 for the surface formed by ab. Using the results shown above with reference to
From this equation, the size of the absorber is calculated (block 640). In this regard, we can solve for A3, which equals A2F21:A2F21=½[(A4+A5)−(A6+A7)], so that
A3=½[(ab′+a′b)−(ab+a′b′)].
In one embodiment, A3 is approximately 0.46 A2 or approximately 0.21 A1. Of course, those skilled in the art will appreciate that these are example values for one embodiment and in no way constitute any limitation.
Next, the surface of the absorber 540 may be drawn using the size calculated. The absorber 540 is drawn by extending the lines a′b′ and ab, and drawing the absorber between the extended lines. It is noted that, while the absorber 540 is illustrated in
Further, the absorber 540 may be oriented in various configurations. As illustrated in
Finally, the design of the concentrator 520 may be completed by connecting the absorber to the aperture (block 650) by drawing the side walls be and b′c′. Referring now to
An edge ray wave front is positioned at the aperture at a predetermined acceptance angle Θ. The wave front is provided with one ring that slides in a manner similar to a shower curtain. One end of a string is connected to the sliding ring at one end of the wave front near point C in
The resulting concentrator exhibits greater efficiency due to a design based on nonimaging optics and thermodynamics. While an optimum concentrator would require that all radiation incident on the aperture also reach the absorber, such a design may be impractical or prohibitively expensive. For example, such a design may result in the hot absorber contacting optical surfaces. In this regard, one embodiment allows some radiation incident on the aperture to miss the absorber to result in an efficient and practical design.
In addition to using non-imaging thermodynamic concentration, further efficiency increase is achieved by embodiments of the present disclosure by forming the concentrator as an internal collector. Internal concentrators take advantage of the benefits of a vacuum insulation.
In the prior art internal concentrator 800, the top of the glass tube 810 forms an aperture having a circular profile. The circular profile of the aperture has several drawbacks. For example, the curvature of the aperture results in refraction of the incoming thermal energy rays. The refraction results in energy losses through, for example, a reduction in the effective acceptance angle of the concentrator. Further, the curvature of the aperture results in the requirement for additional material when compared to a flatter aperture.
Referring now to
The internal concentrator tube 900 further includes an aperture 920 closing the opening of the reflector portion 910. In one embodiment, the aperture 920 and the reflector portion 910 are integrally formed, thus eliminating the need for a seal between the two components. In accordance with embodiments of the present disclosure, the aperture 920 is substantially flat when compared to the reflector portion 910. In this regard, as used herein, substantially flat includes, but is not limited to, a flat surface or an arc with a radius that is substantially larger than half the size of the opening of the reflector portion 910. In various embodiments, the arc has a radius that is between 2 and 20 times half the size of the opening.
In one embodiment, the junction of the reflector portion 910 and the aperture 920 forms a substantially right angle. In various embodiments, the angle formed by the reflector portion 910 and the aperture 920 is between about 60 degrees and about 120 degrees, preferably between about 70 degrees and about 110 degrees, more preferably between about 80 degrees and about 100 degrees, and still more preferably between about 85 degrees and about 95 degrees. The internal concentrator tube 900 of
Thus, the aperture 920 is substantially flat when compared to the reflector portion 910 and when compared to prior art internal concentrators. The flatter configuration minimized or eliminates reduction in the effective acceptance angle due to refraction of the incoming rays of thermal energy. Further, the flatter configuration reduces the amount of material needed to form the glass tube.
The internal concentrator tube 900 further includes an absorber 930 extending the length of the tube 900. The tube is positioned to receive thermal energy reflected from the reflective surface 912. A fluid flowing through the absorber 930 is heated by the thermal energy. The flowing fluid serves to transfer thermal energy to, for example, a manifold connecting a plurality of internal concentrator tubes. Various configurations of the absorber 930 are illustrated and described below with reference to
As illustrated on one end of the internal concentrator tube 900 in
The glass tube 900 may be formed in any of a number of ways, including methods that are well known to those skilled in the art. For example, reference may be made to U.S. Pat. No. 7,475,567, which describes a method for forming a continuous glass tube with a shaping body on the inside of the tube. In one embodiment, the glass tube is formed by pressing a mandrel or mold on the outside of the softened glass tube to shape the tube.
Referring now to
Further, as illustrated in
In accordance with various embodiments, an internal concentrator is formed of a glass tube. The reflector is formed by placing a reflective coating on a part of the internal surface of the glass tube. The reflective coating may be formed by, for example, sputtering silver or aluminum onto the glass tube or by chemical deposition of silver onto the glass tube.
In various embodiments, the thickness of the glass forming the aperture 920 may cause aberrations (e.g., refraction) in the light entering the internal concentrator 900. In this regard, the internal concentrator 900 may be configured to account and correct for such aberrations. In this regard, one example configuration is described below with reference to
Based on the circumference of the absorber 930, the internal length AA′ of the aperture 920 is calculated. This length AA′ is calculated as the circumference of the absorber 930 (RSTS′R) divided by the sine of the incident angle Θ: AA′=(RSTS′R)/sin(Θ).
The slope of the reflector at A′ is chosen to reflect ray A′C to be mirror symmetric to AC′. Thus, AC′ and A′C intersect at the centerline OR. The position of the absorber 930 relative to the aperture 920 is based on the rays entering the internal concentrator 900 on the edges of the aperture 920, AC′ and A′C. The angle or position of symmetric rays AC′ and A′C can be calculated since the rays DB and D′B′ are parallel, having the incident angle Θ and known refractive index of the aperture glass. Thus, assuming the absorber 930 is symmetric, the absorber 930 contacts, but does not cross, the rays AC′ and A′C and is below the intersection of the rays A′C and AC′. Thus, the absorber 930 can be positioned relative to the aperture 920 according to the refracted rays A′C and AC′.
Now, the shape of the reflector portion 910 may be calculated for a configuration to account for aberrations caused by the aperture 920. Starting from position A′ where the reflector slope has been determined, the curve continues with each successive slope reflecting the edge rays from DD′ into rays tangent to the absorber in the usual way. In this way, the method of nonimaging edge ray design can be employed even in the presence of refraction by the glass of the aperture 920. This process can be repeated for all points between A′ and C′. The portion of the reflector from C′ to R is designed to reflect tangent rays from the absorber 930 back on themselves. Thus, the shape of the reflector portion 910 can be calculated based on the refracted rays passing through the glass forming the aperture 920.
Various embodiments may employ absorbers with various form factors. As noted above, in some embodiments, the absorber may have an inlet and an outlet that allow thermal energy transfer fluid to flow through the absorber.
In some embodiments, the absorber may be formed as a u-shaped tube or “u-tube”, where the fluid inlets and outlets are positioned at the same end of the absorber, with a u-shaped flow path connecting the inlet/outlet.
For example,
In some embodiments the channels may be minichannels, having a cross sectional area of less than 1 cm{circumflex over ( )}2, 1 mm{circumflex over ( )}2, 0.1 mm{circumflex over ( )}2, or less.
Accordingly, the concentrator is well suited for non-tracking applications. In other embodiments, concentrators may feature even greater optical efficiency over even wider acceptance angles.
The foregoing description of embodiments has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments. The embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments and its practical application to enable one skilled in the art to utilize the present disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.
One or more or any part thereof of the techniques described herein can be implemented in computer hardware or software, or a combination of both. The methods can be implemented in computer programs using standard programming techniques following the method and figures described herein. Program code is applied to input data to perform the functions described herein and generate output information. The output information is applied to one or more output devices such as a display monitor. Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the programs can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language. Moreover, the program can run on dedicated integrated circuits preprogrammed for that purpose.
Each such computer program is preferably stored on a storage medium or device (e.g., ROM or magnetic diskette) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. The computer program can also reside in cache or main memory during program execution. The analysis method can also be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.
As used herein the term “light” and related terms (e.g. “optical”) are to be understood to include electromagnetic radiation both within and outside of the visible spectrum, including, for example, ultraviolet and infrared radiation.
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
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